Present invention relates to an apparatus and method for determining the distance between skeletal bodies moveable relative to one another for the purpose of affecting a ligament graft between the skeletal bodies.
Natural ligaments, when damaged, require replacement through reconstructive surgery. This process often requires replacement of the natural ligament with a grafted ligament.
In the case of the replacement of the anterior or posterior cruciate ligaments of a the knee, it is extremely important to determine the fixation sites for the graft. Such "isometric" positioning of the grafted ligament requires that the sites on the femur and tibia maintain a substantially constant distance from one another during the flexion and extension of the knee.
In the past, tension isometers have been employed in which graft fixation sites are estimated, drilled, pinned, and connected with a tension string. The tension on the string is measured by rotating the knee. If the sites are not correctly initially determined, redrilling and repinning is required. Such process is cumbersome and not very accurate. In this regard, U.S. Pat. No. 4,712,542 describes a method for establishing ligament graft tension and isometry employing a wire cable or suture through the estimated fixation sites on the femur and tibia.
Reference is also made to articles entitled "Measurement of the Total Motion Between To Body Segments I and II" by Kinzel et al, which describes a linkage using a group of links and potentiometers for ascertaining total motion measurements between body segments having six degrees of freedom.
An apparatus method for determining isometric positioning between the femur and tibia for the grafting of cruciate ligaments of the knee would be a noticeable advance in the medical field.